Microporous membranes possess a number of desirable physical attributes--e.g.,their extremely small pore sizes, gas and liquid permeability, chemical stability, nontoxicity, mechanical strength, and the like--that are useful in many end-use applications. For example, microporous membranes have been employed in blood oxygenation systems, liquid-liquid extraction systems, and microfiltration systems, to name just a few.
U.S. Pat. No. 4,789,468 issued on Dec. 6, 1988 to Sirkar (the entire content of which is expressly incorporated hereinto by reference), discloses a liquid-liquid extraction system which utilizes microporous membranes. In this regard, the system disclosed in this patent relies upon an interface-immobilizing pressure difference effective to prevent the feed liquid from flowing through the micropores of the membrane and dispersing in the extractant liquid on the opposite side of the membrane.
However, as is recognized in U.S Pat. No. 4,789,468, the range of pressure differences effective to immobilize the interface between particular liquids depends on a number of factors, including the physical properties of the liquids employed (e.g., their respective abilities to "wet" the membrane, the interfacial tension between the liquids, and the flow characteristics of the liquids at the surface of the membrane), and the physical attributes of the membranes employed (e.g., the effective size of the membrane pores), which cannot in general be predicted. In this regard, please refer to column 2, line 48 through column 3, line 12 of U.S. Pat. No. 4,789,468.
It might be envisioned, based upon U.S. Pat. No. 4,789,468, that the range of pressure differences for any selected liquids and/or membranes may be predetermined using commercial scale liquid-liquid extraction modules. That is, the range of pressure differences for any selected liquids and/or membranes may be predetermined simply by running tests using full scale liquid-liquid extraction modules so as to establish a maximum pressure difference that can be tolerated by the full scale module. It would, however, clearly be more advantageous if the full scale commercial module could be dedicated to performing only liquid-liquid extractions and thus not employed for any physical testing of the liquids and/or hollow fibers. Thus, it would be highly desirable if the unknowns for any given liquid and/or hollow fiber membrane in a liquid-liquid extraction system could be predetermined using a laboratory bench scale system. It is towards providing such a laboratory bench scale system that the present invention is directed.
According to one aspect of this invention, disposable microporous hollow fiber (sometimes referred to hereinafter simply as "MHF") test modules are provided which include a number of microporous hollow fiber membranes formed into a loop such that opposing ends of the fibers are adjacent to one another. These opposing ends are then positionally retained (e.g., via a suitable potting compound) within a tubular sleeve. The test module may then be coupled operatively to a source of pressurized feed liquid so that the lumens at the adjacent opposing ends are fluid-connected to the same. The loops of MHF are immersed in essentially unpressurized (i.e., at atmospheric pressure) extractant liquid.
The pressure of the feed liquid may then gradually be increased until an incipient presence of the feed liquid appears in the essentially unpressurized extractant liquid. This incipient presence will therefore establish a maximum pressure difference that can be tolerated using the particular feed and extractant liquids and the particular MHF under investigation. As can be appreciated, different feed liquids, extractant liquids, and/or MHF may be investigated simply by providing a "fresh" test module having the desired MHF to be investigated and then operating the system with the desired feed and extractant liquids to be investigated as discussed above. In such a manner, a number of different liquid and/or MHF candidates for liquid-liquid extractions may be screened quickly so that more optimum usage of full scale commercial MHF liquid-liquid extraction modules is realized.
On-line detection of the presence of the essentially immiscible feed liquid in an extractant liquid stream of a liquid-liquid extraction system is also provided by this invention. By detecting the presence of the feed liquid i the extractant liquid on line, any failures and/or malfunctions of a liquid-liquid extraction module employing microporous hollow fibers may quickly be determined so that remedial action can be taken.
These and other aspects and advantages of the invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments.